Numerous types of mechanical logging equipment have been proposed and usually these include some type of cutting mechanism for severing the tree at its base. The most common type of cutter that has been used, particularly in large tree harvesting apparatus is the shear cutter wherein a pair of shear blades are pivoted on a frame and are moved between open and closed positions through drive means, usually in the form of a fluid ram. One of the problems with a shear cutter is that physical force is required to force the sharp edge of the shear through the base of the tree and results in splitting the tree trunk during the severing operation. An example of this type of shear mechanism is disclosed in U.S. Pat. No. 3,575,222.
Another type of cutter that has been proposed is what is commonly referred to as a rotary cutter which is rotated about its own axis and is moved across the base of the tree through some drive mechanism for severing the tree. An example of this type of mechanism is disclosed in U.S. Pat. No. 3,902,538. The problem with the rotary cutter is that initially such cutting units are fairly expensive and also require daily sharpening which decreases the production time and increases the cost per severed tree.
A third type of cutting mechanism is what is commonly referred to as a chain saw which may be mounted on a frame that is movable with respect to a tree. One of the problems encountered with this type of cutting device is that the cutting elements tend to dull rather quickly and are subjected to damage. Another disadvantage is that the cutting apparatus must be rotated in the same direction.
Another type of cutting apparatus that has been known for many years is what is commonly referred to as a cable saw wherein a flexible cable supports a plurality of cutting elements. Examples of this type of saw are disclosed in U.S. Pat. Nos. 641,129; 1,457,761; 1,903,518; 2,043,603; 2,752,964; and 3,958,332.